This invention relates to a swivel joint for use with construction equipment of the upper structure revolving type such as a wheel mounted shovel or a wheel crane for connecting fluid pipes to each other between a lower structure and an upper structure.
The prior art will be described taking a wheel mounted shovel as an example of a construction equipment of the upper structure revolving type.
Referring to FIG. 4, a conventional wheel mounted shovel shown includes a lower structure 1 serving as a lower base and an upper structure 2 carried on the lower structure 1 by way of a pivotal bearing 3, and an engine 4, a tank 5 for working fluid to be supplied to hydraulic devices and a tank 6 for fuel oil to be supplied to the engine 4 are installed on the upper structure 2.
FIG. 5 shows a fuel oil circuit interconnecting the fuel oil tank 6 and the engine 4.
Fuel oil in the fuel oil tank 6 is supplied into a nozzle holder 9 by a feed pump 7 and an injection pump 8 as indicated by solid line arrow marks in FIG. 5. Meanwhile, return oil which overflows from the engine 4 is returned into the fuel oil tank 6 by way of a filter 10 as indicated by broken line arrow marks.
Additionally, FIG. 6 shows a construction of a conventional swivel joint.
The swivel joint 11 shown includes a tubular body 12 and a cylindrical stem 13 fitted for rotation relative to each other around a common axis, and for example, the stem 13 is mounted as a rotary side member on the upper structure while the body 12 is mounted as a fixed side member on the lower structure.
The body 12 is divided in the direction of the axis thereof into two divisional parts including a first divisional body part 14 and a second divisional body part 15 in order to facilitate working and assembly of the swivel joint. The two body parts 14 and 15 are connected in an integrated relationship to each other by means of bolts 16.
A stem side air passage 17a and a stem side working oil passage 18a are provided in the stem 13.
Meanwhile, a pair of body side air and working oil passages 17c and 18c and a pair of body side annular grooves 17b and 18b are provided in the body 12. A pair of air and working oil passages 17 and 18 are thus provided which extend through the body 12 and the stem 13. A plurality of seal members 19 are provided on an inner periphery of the body 12.
Each of the passages 17 and 18 has an end connected to a corresponding pipe not shown on the upper structure 2 side and the other end connected to another corresponding pipe not shown on the lower structure 1 side such that the upper and lower pipes for air and the upper and lower pipes for working oil may be interconnected by way of the swivel joint 11.
It is to be noted that, while such passages 17 and 18 as described above are normally provided each by a plural number, only one of each of them is shown to facilitate illustration and description of the mechanism.
Such a wheel mounted shovel is disadvantageous in that, where the fuel tank 6 is mounted on the upper structure 2 as described above, it is located at an excessively high position, and consequently, a fuel oil supplying operation is cumbersome.
Thus, it may seem convenient to install the fuel oil tank 6 otherwise on the lower structure 1 as shown in FIG. 7 in order to facilitate such a fuel oil supplying operation.
In this instance, a fuel oil supplying pipe for suppling fuel oil from the fuel oil tank 6 to the engine 4 and a return oil pipe for returning return oil to the tank 6 are each divided into upper and lower portions similarly to any other pipe for other fluid such as air and working oil, and the upper and lower portions of the pipes are connected to each other by way of the swivel joint 11. In this instance, if the construction of the fuel oil passages of the conventional swivel joint 11 is employed as it is as passage construction for fuel oil, then this will give rise to the following problem.
In particular, in a swivel joint of the type mentioned, fluid is likely to leak from an annular groove at a junction between fluid passages of the body side and the stem side to a location between fitting faces of the body and stem, and this leaking fluid may be mixed with another leaking fluid or may leak to the outer side.
Accordingly, where such a construction is employed that fuel oil (fuel supply oil and return oil) is delivered between the body and the stem by way of an annular groove in the body similarly as for air and working oil, such other fluid as air or working oil may be mixed with the fuel oil thereby to deteriorate the combustion efficiency, or on the contrary, fluid oil may be mixed into some other fluid thereby to obstruct an original function of the fluid. Or there is a problem that fuel oil may leak to the outer side to bring about a dangerous condition.